Certain fluorocarbon polymer compositions have found use for example as sealants in the manufacture and repair of supersonic aircraft. Liquid curable compositions for this application can be formulated which cure to an elastomeric state over a period of a few days at ambient temperatures of about 18.degree. to 20.degree. C. or more quickly at higher temperatures. For example, there are disclosed in UK patent specification No. 1037672 two-part curable fluorocarbon polymer compositions comprising a copolymer of hexafluoropropylene with vinylidene fluoride, magnesium oxide, amines, 1:6 hexane-dithiol and a silane. The dithiol is a significantly malodorous material, but for many years has been regarded as an important ingredient for the curing of the polymer. Presence of a dithiol in the composition has been regarded as essential in order to achieve compositions which have an adequate "work life" when mixed and are capable of curing to an elastomeric state at room temperature, and of adhering satisfactorily to materials used in aircraft construction for example alloys of titanium and chromate treated or epoxy coated aluminium alloys. Curable compositions using fluorocarbon polymer and dithiol have been used for many years, but it is believed that their offensive odour has inhibited more extensive use of the compositions, especially for example where the composition is required to be mixed or applied in a confined working space, or applied to large areas of a workpiece.
Odourless compositions are highly desirable, coupled with the ability to remain usable for a desired length of time after mixing and then become cured to an elastomeric state within an acceptably short time, without application of heat. Not only is it desirable to identify a composition of low odour, and suitable cure characteristics, but also it is necessary to provide a means of achieving good adhesion to metal alloys (for example ones based on titanium or aluminium) which are used in the aircraft construction industry, without promoting unacceptable corrosion of the metal alloys. As far as we are aware, prior to the present invention, no composition has been proposed which satisfied these requirements.